The present invention relates in general to press brake machines, and more particularly to an automated control and actuator system for such machines whereby press strokes of various predetermined limits and speeds can be automatically accomplished in sequence.
Press brake machines generally consist of an upstanding frame to the bottom end of which a horizontal bed plate is mounted, and to the top end of which a pair of hydraulic cylinders are mounted to reciprocatively drive a ram downward against the bed. In operation, the ram and bed are fitted with coacting dies and a work piece to be formed or sheared is placed between the dies. Upon actuation of a hand-controlled switch or foot pedal by the operator, hydraulic power is supplied to the cylinders to bring the ram down with sufficient force to cause the dies to perform the desired forming or shearing operation.
In practice, it is frequently desirable to perform successive bending operations on a sheet metal work peice wherein one or more bends are made with the upper movable die advancing and retracting to particular predetermined locations with respect to the lower fixed die, and wherein one or more additional bends are made with the movable die advancing and retracting to different predetermined locations relative to the lower die. Moreover, it is desirable that the sequence of bending operations be accomplished automatically, without the need for the operator to effect a different set-up prior to each bending operation.
For optimum operating efficiency, it is also desirable that the ram advance initially at a relatively fast speed until the upper die nears contact with the work piece, then slow to a lower pressing speed as the die actually engages the work piece and performs the desired forming or shearing operation. Furthermore, it is desirable that the ram pressing speed be varied according to the demands of the particular bending or shearing operation being performed. For example, it is often possible to advance the ram at a higher pressing speed for a shallow bend in relatively light gauge material, whereas a slower pressing speed is required for acute bends in heavy gauge material.
Various automatic control systems have been provided for obtaining one or more of these operational features in prior art programmable hydraulic press brake machines. However, such systems have typically been in the form of "add on" basically "open loop" systems intended to take the place of the multiple limit switches provided for ram control on the press brakes, and as such have not provided the degree of programminng flexibility and ram control obtained with the present system.
In contrast, in the apparatus of the present invention, which operates on a continuous closed loop principle, length of down stroke, length of return stroke, length of pressing stroke, and pressing speed parameters are all automatically established for each stroke in a multi-stroke pressing operation without the necessity for intervening operator adjustment. In addition, the apparatus of the present invention provides means whereby these parameters can be readily programmed, and whereby modifications in the program including the repeat of one or more strokes in the pressing operation can be readily accomplished. Moreover, the apparatus of the invention has the ability to idle or hold the ram stationary at any desired position along its path of travel, and to maintain the ram level notwithstanding load variations during the pressing stroke.